Structure of the Transition Region and the Low Corona from TRACE and SDO Observations Near the Limb

Alissandrakis, C. E.; Valentino, A.

doi:10.1007/s11207-019-1486-7

Cited by 8 publications

(5 citation statements)

References 32 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…8). Given now that models and observations show that AIA 1600 Å forms below ALMA 3 mm (e.g., Shibasaki et al 2011;Howe et al 2012;Wedemeyer et al 2016;Alissandrakis et al 2017;Alissandrakis and Valentino 2019), our results imply upward propagating waves, consistent with p-mode propagation throughout the chromosphere. The decreasing relative rms of the p-mode oscillation in going from 1600 Å to ALMA 3 mm is also consistent with this assertion.…”

Section: Time-lag Analysissupporting

confidence: 81%

“…Our findings regarding the height-separation between the ALMA 3 mm and AIA 1600 Å formation layers are consistent with related observational and modeling work. Empirical modeling of the solar atmosphere indicates that 1600 Å forms at a height of ≈ 500-750 km (Shibasaki et al 2011), whereas, analysis of TRACE observations of the 1999 Mercury transit showed a peak height of 500 km and a limb height of 1200 km (Alissandrakis and Valentino 2019). Radiation-hydrodynamics modeling of a broadband spectrum of acoustic waves yields a formation height of the 1600 Å channel of TRACE, with similar wavelength response to the corresponding AIA channel, of 430 ± 185 km (Fossum and Carlsson 2005).…”

Section: Time-lag Analysismentioning

confidence: 93%

See 1 more Smart Citation

Observations of solar chromospheric oscillations at 3 mm with ALMA

Patsourakos

Alissandrakis

Nindos

et al. 2020

A&A

Self Cite

View full text Add to dashboard Cite

Aims. To study spatially-resolved chromospheric oscillations of the quiet Sun in the mm-domain at a resolution of a few arcsec, typically 2.4 ×4.5 . Methods. We used Atacama Large millimeter and sub-millimeter Array (ALMA) time-series of interferometric observations of the quiet Sun obtained at 3 mm with a 2-s cadence and a spatial resolution of a few arcsec. The observations were performed on March 16, 2017 and seven 80 ×80 fields-of-view going from disk center to limb were covered, each one observed for 10 min, therefore limiting the frequency resolution of the power spectra to 1.7 mHz. For each field of view, masks for cell and network were derived, and the averaged power spectral densities (PSDs) for the entire field of view, cell and network were computed. The resulting power spectra were fitted with an analytical function in order to derive the frequency and the root-mean-square (rms) power associated with the peaks. The same analysis, over the same fields of view and for the same intervals, was performed for simultaneous Atmospheric Imaging Assembly (AIA) image sequences in 1600 Å. Results. Spatially-resolved chromospheric oscillations at 3 mm, with frequencies of 4.2 ± 1.7 mHz are observed in the quiet Sun, in both cell and network. The coherence length-scale of the oscillations is commensurate with the spatial resolution of our ALMA observations. Brightness-temperature fluctuations in individual pixels could reach up to a few hundred K, while the spatially averaged power spectral densities yield rms in the range ≈ 55-75 K, i.e., up to ≈ 1 % of the averaged brightness temperatures and exhibit a moderate increase towards the limb. For AIA 1600 Å the oscillation frequency is 3.7 ± 1.7 mHz. The relative rms is up to 6% of the background intensity, with a weak increase towards disk center (cell, average). ALMA 3 mm time-series lag AIA 1600 Å by ≈ 100 s, which corresponds to a formation-height difference of ≈ 1200 km, representing a novel determination of this important parameter. Conclusions. The ALMA oscillations that we detected exhibit higher amplitudes than those derived from the lower (≈ 10 ) resolution observations at 3.5 mm by White et al. (2006). Chromospheric oscillations are, therefore, not fully resolved at the length-scale of the chromospheric network, and possibly not even at the spatial resolution of our ALMA observations. Any study of transient brightenings in the mm-domain should take into account the oscillations.

show abstract

Section: Time-lag Analysissupporting

confidence: 81%

Section: Time-lag Analysismentioning

confidence: 93%

Observations of solar chromospheric oscillations at 3 mm with ALMA

Patsourakos

Alissandrakis

Nindos

et al. 2020

A&A

Self Cite

View full text Add to dashboard Cite

show abstract

“…Modelling work has predicted coronal scale heights on the order of 30–60 Mm (approx. 30 000–50 000 km; [71–73]), so an initial comparison would suggest that the measured coronal damping lengths are much shorter than typical coronal scale heights (by at least an order of magnitude). However, recent theoretical work has calculated the expected coronal damping lengths using classical Spitzer values for thermal conduction and predicted much longer damping lengths than observed in coronal loops [67], hence suggesting either a lack of sensitivity in current coronal observations, or ill-constrained values of thermal conduction in current modelling efforts.…”

Section: Discussionmentioning

confidence: 99%

Magnetoacoustic wave energy dissipation in the atmosphere of solar pores

Gilchrist-Millar

Jess

Grant

et al. 2020

Phil. Trans. R. Soc. A.

View full text Add to dashboard Cite

The suitability of solar pores as magnetic wave guides has been a key topic of discussion in recent years. Here, we present observational evidence of propagating magnetohydrodynamic wave activity in a group of five photospheric solar pores. Employing data obtained by the Facility Infrared Spectropolarimeter at the Dunn Solar Telescope, oscillations with periods of the order of 5 min were detected at varying atmospheric heights by examining Si ɪ 10827 Å line bisector velocities. Spectropolarimetric inversions, coupled with the spatially resolved root mean square bisector velocities, allowed the wave energy fluxes to be estimated as a function of atmospheric height for each pore. We find propagating magnetoacoustic sausage mode waves with energy fluxes on the order of 30 kW m −2 at an atmospheric height of 100 km, dropping to approximately 2 kW m −2 at an atmospheric height of around 500 km. The cross-sectional structuring of the energy fluxes reveals the presence of both body- and surface-mode sausage waves. Examination of the energy flux decay with atmospheric height provides an estimate of the damping length, found to have an average value across all five pores of L d ≈ 268 km, similar to the photospheric density scale height. We find the damping lengths are longer for body mode waves, suggesting that surface mode sausage oscillations are able to more readily dissipate their embedded wave energies. This work verifies the suitability of solar pores to act as efficient conduits when guiding magnetoacoustic wave energy upwards into the outer solar atmosphere. This article is part of the Theo Murphy meeting issue ‘High-resolution wave dynamics in the lower solar atmosphere’.

show abstract

“…These authors noted the presence of "sawtooth" irregularities on the limb and jet-like activity that appeared to correspond well to IRIS "jet clusters". Interestingly, these limb irregularities seen at 3 mm were well-correlated with absorption observed in the SDO 171Å band; i.e., the EUV emission from plasma at coronal temperatures was absorbed by foreground chromospheric structures (see also Alissandrakis and Valentino, 2019). A dynamic feature rising at 40 km-s −1 , showing a brightness excess of just 135 K was determined to have an electron density of 4.6-8.4 × 10 9 cm −3 .…”

Section: Observations Of Spiculesmentioning

confidence: 60%

The quiet sun at mm wavelengths as seen by ALMA

Alissandrakis

Bastian²,

Brajša³

2022

Front. Astron. Space Sci.

View full text Add to dashboard Cite

Solar observations at sub-mm, mm and cm wavelengths offer a straightforward diagnostic of physical conditions in the solar atmosphere because they yield measurement of brightness temperature which, for optically thick features, equals intrinsic temperature - much unlike solar diagnostics in other spectral ranges. The Atacama Large Millimeter and sub-millimeter Array (ALMA) has therefore opened a new, hitherto underexplored, spectral window for studying the enigmatic solar chromosphere. In this review we discuss initial ALMA studies of the quiet chromosphere that used both single-dish and compact-array interferometric observing modes. We present results on the temperature structure of the chromosphere, comparison with classic empirical models of the chromosphere, and observations of the chromospheric network and spicules. Furthermore, we discuss what may be expected in the future, since the ALMA capabilities continuously expand and improve towards higher angular resolution, wavelength coverage, and polarization measurement for magnetometry.

show abstract

Structure of the Transition Region and the Low Corona from TRACE and SDO Observations Near the Limb

Cited by 8 publications

References 32 publications

Observations of solar chromospheric oscillations at 3 mm with ALMA

Observations of solar chromospheric oscillations at 3 mm with ALMA

Magnetoacoustic wave energy dissipation in the atmosphere of solar pores

The quiet sun at mm wavelengths as seen by ALMA

Contact Info

Product

Resources

About